Modern demands upon energy conservation and particularly efficient utilization of water resources make it imperative that irrigation or sprinkler installations be operated with a minimum of external power and be capable of uniform distribution of water precisely over the area or pattern to be irrigated. In order to achieve maximum water efficiency in a sprinkler installation, the water stream must be confined to the contour or area which requires watering and must be uniformly distributed over that area. Various sprinkler systems have been designed which are capable of being adjustable or conformable to different contours or patterns to be sprinkled and these generally take the approach of a rotatable pop-up type sprinkler head having multi-hole nozzle assemblies which are rotated and, as the area or radial distance away from the sprinkler head is either increased or reduced a greater or lesser number of nozzle holes are open for the discharge of water. Typical of this approach is U.S. Letters Patent to Taylor U.S. Pat. No. 3,952,954 wherein an automatic sprinkler has a plurality of fingers which are bent to vary the radius of the spray as a function of its rotation, and a speed control unit having a positive displacement hydraulic brake varies the rotational speed of the sprinkler according to the area of lawn being watered at any given time. U.S. Letters Patent to Carlson U.S. Pat. No. 3,575,347 employs a cam controlled nozzle assembly in a sprinkler head in which a plate has a stair-step configuration and can be progressively advanced across the ends of the nozzle openings to control the area over which the stream is discharged from the nozzle assembly. Other patents which take similar approaches to Carlson are Olson U.S. Pat. No. 3,960,327; Hurley U.S. Pat. No. 2,805,098; Martin U.S. Pat. No. 2,414,052 and Mullan U.S. Pat. No. 3,405,871 as well as the patent to Karbo U.S. Pat. No. 3,452,930. For example, Karbo utilizes a plurality of pins as cam control elements in which the radial position of the pins will control the pattern of water discharged by the sprinkler head.
U.S. Letters Patent to Dagaro U.S. Pat. No. 3,398,894 is directed to an automatic sprinkler having an adjustable cam-controlled spray, while the patent to Barnes U.S. Pat. No. 3,362,641 discloses a plurality of nozzles in a sprinkler head which are progressively opened or blocked by a piston as the piston is raised or lowered by linkage connected to a water operated motor drive. Rothweiler U.S. Pat. No. 2,731,294 also discloses a sprinkler head having a nozzle assembly in which the nozzle orifices are inclined at various angles so as to produce jets of water which strike the ground at various distances from the sprinkler head. None of these arrangements, however, disclose a system which is capable of establishing uniform water distribution notwithstanding variations in the area or pattern sprayed as the sprinkler head is continuously rotated and particularly in such a way as to effect distribution in that area immediately surrounding the sprinkler head; and at the same time it is desirable that the nozzle assembly can be closely controlled to undergo rapid variations in the amount and pattern of water distributed while assuring smooth transition in the flow and pattern of water discharged at closely spaced circumferential intervals throughout each full revolution.
Moreover, in order to minimize external power requirements while assuring maximum utilization of the water, it is highly desirable that the sprinkler heads be connected in series to a common water supply line. Not only does this eliminate considerable installation time and labor in running individual lines to different points of an area to be irrigated from a common water supply source, but also eliminates necessity for a separate timer control at the water source in cycling water successively through each individual line. Previously, systems have been designed in which a plurality of sprinkler heads are series-connected to a common line, such as, U.S. Letters Patent to Chauvigne U.S. Pat. No. 3,964,685 where each sprinkler head in the line has a clapper type valve which is responsive to the volume and pressure of fluid to automatically cut each sprinkler head off and to divert the water to the next successive sprinkler head. In this relation, it is desirable that the cycle of each series-connected sprinkler head be controlled independently of fluid flow or pressure at each head and where the timer system at each head can be accurately regulated and controlled without an external power source; and further to do so in such a way that the timer control for each head is operated directly off the power drive of a contour controlled sprinkler.